The heart is a four-chambered pump that moves blood efficiently through the vascular system. Blood enters the heart through the vena cava and flows into the right atrium. From the right atrium, blood flows through the tricuspid valve and into the right ventricle, which then contracts and forces blood through the pulmonic valve and into the lungs. Oxygenated blood returns from the lungs and enters the heart through the left atrium and passes through the mitral valve into the left ventricle. The left ventricle contracts and pumps blood through the aortic valve into the aorta and to the vascular system.
The mitral valve consists of two leaflets (anterior and posterior) attached to a fibrous ring or annulus. In a healthy heart, the mitral valve leaflets close during contraction of the left ventricle and prevent blood from flowing back into the left atrium. Due to various cardiac diseases, however, the mitral valve annulus may become distended, causing the leaflets to remain partially open during ventricular contraction and thus allow regurgitation of blood into the left atrium. This results in reduced ejection volume from the left ventricle, causing the left ventricle to compensate with a larger stroke volume. The increased workload eventually results in dilation and hypertrophy of the left ventricle, further enlarging and distorting the shape of the mitral valve. If left untreated, the condition may result in cardiac insufficiency, ventricular failure, and ultimately death.
It is common medical practice to treat mitral valve regurgitation by either valve repair or replacement. Mitral valve repair includes a variety of procedures to repair or reshape the leaflets to improve closure of the valve during ventricular contraction. If the mitral valve annulus has become distended, a frequent repair procedure involves implanting an annuloplasty ring on the mitral valve annulus. The annuloplasty ring generally has a smaller diameter than the annulus, and when sutured to the annulus the annuloplasty ring draws the annulus into a smaller configuration, bringing the mitral valve leaflets closer together and allowing improved closure during ventricular contraction. Annuloplasty rings may be rigid, flexible or a combination, having both rigid and flexible segments. Rigid annuloplasty rings have the disadvantage of causing the mitral valve annulus to be rigid and unable to flex in response to the contractions of the ventricle, thus inhibiting the normal, three-dimensional movement of the mitral valve that is required for it to function optimally. Flexible annuloplasty rings are frequently made of Dacron® fabric and must be sewn to the annulus tissue with a line of sutures. This eventually leads to scar tissue formation and loss of flexibility and function of the mitral valve. Similarly, combination rings must generally be sutured in place and also cause scar tissue formation and loss of mitral valve flexibility and function. Annuloplasty is normally an open-heart surgical procedure.
Valve replacement also typically entails an open-heart surgical procedure in which the patient's mitral valve is removed and replaced with an artificial valve. One drawback to open-heart surgical techniques is that heart bypass procedures are required to accomplish replacement and/or repair of the valve. Another drawback is that the open-heart procedures require that the patient undergo general anesthesia for a prolonged period of time.
To overcome many of the complications and risks of open-heart surgical procedures, less invasive or minimally invasive surgical techniques have been developed. These procedures can be done on a beating heart and often are performed without general anesthesia or a reduced time under general anesthesia.
More recently, mitral and other cardiac valve annuloplasty devices and procedures have been developed that employ a helical anchor coil in place of the conventional annuloplasty rings (or bands). Examples of such devices and procedures are described, for example, in US Publication Nos. 2007/0244553, 2007/0244554, 2007/0244555, 2007/0244556, and 2007/0244557, each of which is incorporated by reference herein in its entirety. In general terms, one or more helical anchor coils are percutaneously delivered, in a coiled state, to the mitral valve annulus via a tubular delivery member. The helical anchor has a sharpened tip that penetrates into tissue of the valve annulus; as the helical anchor is directed out of the delivery member and rotated along a guide, the helical anchor threads into the annulus tissue. A tether is routed through an inner channel of the so-implanted helical anchor(s) and formed into a loop. The loop is tensioned, effectuating a desired modification in the shape of the valve annulus.
The helical anchor and tether systems described above are quite promising, simulating the surgical placement of an annuloplasty ring on the valve annulus. However, the described minimally invasive delivery techniques may be less than optimal. Further, any improvements in the helical anchor coils and related methods of use will be well-received.